It is general prior art practice, in connecting central offices or nodes via area exchange trunks, at any given node to drop and add circuits, access and patch circuits through to the next office or node. One way of accomplishing these functions is to use a so-called drop and insert configuration in which channel multiplexers are placed back to back and through channels patched through and dropped channels are made available.
In a ring network in which channels are added or dropped at each node of the ring, using the above described type of equipment, the state of the art approach is to use the drop/insert configuration. In order to insure that the transmission between nodes or central offices is reliable, a redundant transmission scheme is used employing a so-called 1.times.1 protection approach. Such an approach (see FIG. 1) contemplates that in each node, channels are dropped and inserted using back-to-back multiplexers with dropping and patching of channels as desired to serve the required capacity of the equipment located at each node. Outputs of each multiplexer/demultiplexer are transmitted through redundant paths by bridging the signal at the transmit end and selecting the best channel at the received end via a "protection" switch. Thus, failure of a transmitter or a receiver or a communications path between nodes will not result in an outage. However, a loss of both communications paths (due to a cable cut or other path interruption), between nodes will result in an outage. To protect against such an outage, an elaborate central control node is used, which controls protection switching and bypass mechanisms at each node. However, such implementations have reliability problems of their own due to the complexity of the control node.
Prior art ring networks for data and voice communication require costly equipment, are designed to minimize transmission band width and employ a large amount of equipment (back-to-back multiplexers in a drop/insert configuration). A communication system using less equipment which would not result in an outage if an entire cable were cut (without the use of a central control node) would represent a significant step forward in the art. It is towards these ends that the present invention is addressed.